The colossal squid (Mesonychoteuthis hamiltoni, from Greekmesos (middle), onycho (claw, nail), and teuthis (squid)), sometimes called the Antarctic or giant cranch squid, is believed to be the largest squid species in terms of mass. It is the only known member of the genusMesonychoteuthis. It is known from only a few specimens, and current estimates put its maximum size at 12–14 m (39–46 ft) long and weighing possibly up to 750 kg (1,650 lb),[1][2] based on analysis of smaller and immature specimens, making it the largest known invertebrate.

Unlike the giant squid, whose arms and tentacles have only suckers lined with small teeth, the colossal squid's limbs are also equipped with sharp hooks: some swivelling, others three-pointed.[3] Its body is wider and stouter, and therefore heavier, than that of the giant squid. Colossal squid are believed to have longer mantles than the giant squid, but shorter tentacles.

The squid exhibits abyssal gigantism. The beak of M. hamiltoni is the largest known of any squid, and more robust than that of the giant squid. The colossal squid also has the largest eyes documented in the animal kingdom; a partly collapsed specimen measured 27 cm (11 in) in diameter, with a 9 cm (3.5 in) pupil.[4][5] The eye was estimated to be 30 to 40 cm (12 to 16 in) when the squid was alive.

Little is known about the life of this creature, but it is believed to feed on prey such as chaetognatha, large fish such as the Patagonian toothfish, and other squid in the deep ocean using bioluminescence. A recent study by Remeslo, Yakushev and Laptikhovsky revealed that Antarctic toothfish make up a significant part of the colossal squid's diet; of the 8,000 toothfishes brought aboard trawlers between 2011 and 2014, 71 showed clear signs of attack by colossal squid.[6] The colossal squid is thought to have a slow metabolic rate, needing only around 30 grams (1.1 oz) of prey daily.[7] Estimates of its energetic demands suggest it is a slow-moving ambush predator, using its large eyes primarily for predator detection rather than active hunting.[7][8]

Based on capture depths of a few specimens, and beaks found in sperm whale stomachs, the adult colossal squid ranges at least to a depth of 2.2 km (7,200 ft), and juveniles can go as deep as 1 km (3,300 ft). It is believed to be sexually dimorphic, with mature females generally being much larger than mature males, as is common in many species of invertebrates.

The squid's method of reproduction has not been observed, although some data on their reproduction can be inferred from anatomy. Since males lack an organ called a hectocotylus (an arm used in other cephalopods to transfer a spermatophore to the female), they probably use a penis instead, which would be used to directly implant sperm into females.

The species was first discovered in the form of two tentacles found in the stomach of a sperm whale in 1925.[11] In 1981 a Russian trawler in the Ross Sea, off the coast of Antarctica, caught a large squid with a total length of 4 m (13 ft), which was later identified as an immature female of M. hamiltoni.[12] In 2003 a complete specimen of a subadult female was found near the surface with a total length of 6 m (20 ft) and a mantle length of 2.5 m (8.2 ft).[13] This specimen shows that colossal squids may grow larger than 500 kg (1,100 lb), possibly up to 750 kg (1,650 lb).[1]

In 2005 a specimen was captured at a depth of 1,625 m (5,331 ft) while taking a toothfish from a longline off South Georgia Island. Although the mantle was not brought aboard, the mantle length was estimated at over 2.5 m (8.2 ft), and the tentacles measured 2.3 m (7.5 ft). The animal is thought to have weighed between 150 and 200 kg (330 and 440 lb).[14]

The largest recorded specimen was captured in 2007 by a New Zealand fishing boat off Antarctica. It was initially estimated to measure 4.5 m (15 ft) in length and weigh 450 kg (990 lb). The squid was taken back to New Zealand for scientific study.[15] A study on the specimen later showed its actual weight was 495 kg (1,091 lb), but it only measured 4.2 m (14 ft) in total length as a result of the tentacles' shrinking post mortem.[16]

This specimen, caught in early 2007, is the largest cephalopod ever recorded. Here it is shown in its live state during capture, with the delicate red skin still intact and the mantle characteristically inflated.

On February 22, 2007, authorities in New Zealand announced the largest known colossal squid had been captured. The specimen weighed 495 kg (1,091 lb) and was initially estimated to measure 4.5 m (15 ft) in total length.[17] Fishermen on the vessel San Aspiring, owned by the Sanford Seafood Company, caught the animal in the freezing Antarctic waters of the Ross Sea. It was brought to the surface as it fed on an Antarctic toothfish that had been caught off a long line. It would not let go of its prey and could not be removed from the line by the fishermen, so they decided to catch it instead. They managed to envelop it in a net, haul it aboard, and freeze it. The specimen eclipsed the previous largest find in 2003 by about 195 kg (430 lb),[18][19] although it is still considerably smaller than some estimates have predicted. The specimen was frozen in a cubic metre of water and transported to the Museum of New Zealand Te Papa Tongarewa, New Zealand's national museum.[20][21] Media reports suggested scientists at the museum were considering using a giant microwave to defrost the squid because defrosting it at room temperature would take days and it would likely rot on the outside while the core remained frozen.[20] However, they later opted for the more conventional approach of thawing the specimen in a bath of salt water.[22][23] After thawing, the squid measured only 4.2 m (14 ft) in total length, with the tentacles having shrunk significantly.[16] Although initially thought to be a male, closer inspection of the specimen showed it to be a female.[5]

The beak is considerably smaller than some found in the stomachs of sperm whales,[24][25] suggesting other colossal squid are much larger than this one.[24][25]

The eye is 27 cm (11 in) wide, with a lens 12 cm (4.7 in) across. This is the largest eye of any known animal.[4] These measurements are of the partly collapsed specimen; when living the eye was probably 30[5] to 40 cm (12 to 16 in) across.[26]

Inspection of the specimen with an endoscope revealed ovaries containing thousands of eggs.[5]

^ abRosa, R. & B.A. Seibel 2010. Slow pace of life of the Antarctic colossal squid. Journal of the Marine Biological Association of the United Kingdom, published online on April 20, 2010. doi:10.1017/S0025315409991494

^"The Colossal Squid Exhibition - Exhibition". tepapa.govt.nz. Retrieved 2012-03-15. The colossal squid is due for a check-up in March this year. We'll assess her condition and decide how long she can safely stay on display. She'll be with us until at least August 2012